Mutarotation, monosaccharide structure

Monosaccharides commonly form internal hemiacetals or hemiketals, in which the aldehyde or ketone group joins with a hydroxyl group of the same molecule, creating a cyclic structure this can be represented as a Haworth perspective formula. The carbon atom originally found in the aldehyde or ketone group (the anomeric carbon) can assume either of two configurations, a and /3, which are interconvertible by mutarotation. In the linear form, which is in equilibrium with the cyclized forms, the anomeric carbon is easily oxidized. 

MUTAROTATION The a- and /T forms of monosaccharides are readily interconverted when dissolved in water. This spontaneous process, called mutarotation, produces an equilibrium mixture of a- and /1-forms in both furanose and pyranose ring structures. The proportion of each form differs with each sugar type. Glucose, for example, exists primarily as a mixture of a- (38%) and j8- (62%) pyranose forms (Figure 7.11). Fructose is predominantly found in the a-and /J-furanose forms. The open chain formed during mutarotation can participate in oxidation-reduction reactions. 

See also Sugar Ring Structures, Derivatives of Monosaccharides, Oligosaccharides, Polysaccharides, Anomers, Ouabain, Amygdalin, Mutarotation... 

Studies have been made on the ring structures of hextdoses and on the mutarotation of monosaccharides by using g.l.c. and m.s. of the per-O-trimethylsilyl derivatives. 

In the crystalline state, reducing monosaccharides exist exclusively in cyclic structures (a- or P-anomers). In solutions, a balance between the a- and P-anomers and acyclic forms is established as the individual forms interconvert over time. This process, schematically shown in Figure 4.2, is called mutarotation. The mechanism of mutarotation assumes cleavage of the saccharide cyclic forms... 

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